The present disclosure is related to films for use in protecting substrate surfaces from damage or contamination. More specifically, the disclosure concerns surface protection films that are free of adhesive coatings, yet offer high adhesion with the substrate, particularly substrates having a textured surface topography.
Surface protection films, also referred to as masking films, are used in numerous applications as a protective covering for surfaces. Typically, the films are used to protect smooth, relatively rigid surfaces, such as acrylics, polycarbonates, glass, polished or painted metals, glazed ceramics, and other smooth, relatively rigid surfaces. The film is applied to the surface to be protected and acts as a physical barrier to prevent scratching, scuffing and marring of the surface. Protection provided by masking films is particularly useful while these surfaces are being printed, transported, or otherwise handled prior to use.
Traditionally, protection for smooth surfaces has been provided via corona treated films and/or adhesive coated masking paper. However, disadvantages exist with these techniques. For example, it is difficult to control the amount of corona treatment to provide good adhesion, yet good release properties. In addition, corona treated masking films have a relatively high surface coefficient of friction and tend to form rigid wrinkles in the film. Such wrinkles are difficult, if not impossible, to remove, thus precluding the film from adequately protecting the surface to be protected and/or permanently distorting the surface to be protected. Also, corona treated polyethylene films commonly have numerous large gels and carbon specks associated with them which can produce dimples in, or otherwise mar, the surface to be protected.
Disadvantages are also associated with masking films using an adhesive coated paper. Moisture from humidity or elsewhere can permeate the masking material and loosen or completely separate the masking material from the surface to be protected. The tendency for moisture to adversely affect the performance of this type of masking film is increased where heat is required to activate the adhesive coating. Additionally, even where the masking material remains firmly adhered to the surface to be protected until its removal is desired, such removal can require the use of a solvent to remove trace amounts of the adhesive coating. The adhesive residue left behind on the surface is of particular concern where the surface being protected is to be used in a context where sanitary conditions are desired, such as in food industry applications.
Recent advances in masking film technology have produced improved masking films formed without corona treatment or the use of adhesive coatings, including one side smooth, one side matted (“OSM”) masking films. Such OSM films are more fully described in U.S. Pat. Nos. 4,895,760 and 5,100,709, the disclosures of which are incorporated herein by reference. These advanced masking films rely upon the tendency for smooth surfaces to adhere to each other to produce an adequate and constant level of adhesion without the need for corona treatment and the use of adhesive coatings. Additionally, the matted side of the OSM films prevents blocking and wrinkling of such films by preventing a measure of intimate contact between the surfaces.
Despite the advanced nature of the OSM films, however, it was discovered that the level of adhesion produced by these improved masking films can vary with temperature and other conditions associated with the production and use of such improved films. At times, such conditions can result in a masking film exhibiting either too much or not enough adhesion level for the desired application. In other applications, it can result in the need for heaters to raise the temperature of the film so that proper application and adequate adhesion level are achieved. Moreover, because the level of adhesion produced is primarily a function of the interaction between the smooth surface of the masking film and the smooth surface to be protected, the smoothness of the surface requiring protection is a significant factor. This factor can present difficulties, and masking films of this type are of limited utility, where the surface to be protected is not particularly smooth, that is, the surface has a textured topography.
Multilayer masking films also have been coextruded with pressure-sensitive adhesive, as described in U.S. Pat. Nos. 5,286,781 and 5,427,850. These films use styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-butadiene (SB), and styrene-isoprene (SI) block copolymers. These block copolymers have poor heat and aging stability due in part to the presence of double bonds. These films also contain anti-blocking agents to provide good unwinding ability, to reduce the rise in tackiness and to prevent the film from laminating to itself while stored in rolls. The anti-blocking agent can migrate (bloom) with temperature and time to ultimately contaminate the substrate surface. Varying levels of anti-blocking agent also results in varying levels of adhesion to the substrate.
There remains a need for a masking film capable of providing an adequate level of protection to surfaces that are textured. There is further a need to provide a functional, adjustable and controlled level of adhesion between the masking film and the textured surface to be protected without the use of corona treatment or an adhesive and their associated disadvantages and under a variety of production and application conditions.